Cuprizone administration in mice provides a reproducible model of demyelination and

Cuprizone administration in mice provides a reproducible model of demyelination and spontaneous remyelination, and has been useful in understanding important aspects of human disease, including multiple sclerosis. assessed histologically. Our results show that demyelination was not limited to the midsagittal line of the corpus callosum, and also that opposing gradients of demyelination occur in the lateral and medial CC. T2-weighted MRI gray/white matter contrast was strong at baseline, weak after 6 weeks of cuprizone treatment, and returned to a limited extent after recovery. MTR decreases during demyelination were observed throughout the brain, most clearly in callosal white matter. Myelin damage and repair appear to be influenced by proximity to oligodendrocyte progenitor cell populations and exhibit an inverse correlation with myelin basic protein gene expression. These findings suggest that susceptibility to injury and ability to repair vary across the brain, and whole-brain analysis is necessary to accurately characterize this model. Whole-brain parametric mapping across time is essential for gaining a real understanding of disease processes in-vivo. MTR increases in healthy mice throughout adolescence and adulthood were observed, illustrating the need for appropriate age-matched controls. Elucidating the unique and site-specific demyelination in the cuprizone model may offer new insights into in mechanisms of both damage and repair in human demyelinating diseases. Introduction Cuprizone [bis-cyclohexanone-oxaldihydrazone] is a low molecular weight copper chelator that induces reversible demyelination in both gray and white matter in the murine brain when added to chow in low concentrations for short periods. First described as a neurotoxin in rodents in the 1960s, cuprizone reliably produces toxic effects including demyelination, hydrocephalus, and astrogliosis.[1,2] The cuprizone mouse captures some aspects of multiple sclerosis (MS), providing a model of demyelination and spontaneous remyelination. AST-1306 Non-focal demyelinating lesions AST-1306 in this model occur in the presence of microglial activation and oligodendrocyte apoptosis without lymphocytic infiltration, which can occur in some MS lesions.[3,4] While cuprizone administration in the mouse has become a common approach used to study demyelination and remyelination processes relevant to human disease, the mechanism of cuprizone action and subsequent oligodendrocyte death is not well understood. Recent reports suggest cuprizone does not accumulate in the brain;[5] rather, cuprizone toxicity extensively modifies copper and zinc distribution in the brain, resulting in mitochondrial dysfunction that leads to demyelination.[6C9] Spatial heterogeneity in brain pathology in the cuprizone model has been demonstrated,[10C15] and the mechanism of demyelination may AST-1306 vary across structures. Because histological analyses are invasive and time-intensive, noninvasive imaging techniques are well suited to complement histology and provide a more comprehensive perspective of pathophysiology, particularly with respect to longitudinal studies. Careful histological analyses are important to validate emerging quantitative and semi-quantitative in-vivo imaging techniques. Several magnetic resonance imaging (MRI) based methods of non-invasively quantifying demyelination in-vivo in the cuprizone mouse model have been explored.[16C21] Magnetization Transfer (MT) has been widely used as a fast and AST-1306 precise measurement capable of semi-quantitative estimation of macromolecular content by calculating the MT ratio (MTR). Myelin content correlates with MTR, but, axonal density and other tissue components can also influence MTR values.[22] PEPCK-C Due to signal-to-noise (SNR) limitations, particularly when imaging small rodents, in-vivo MRI experiments tend to utilize single- or multi-slice acquisitions with thick slices (0.5C1.0mm) and limited coverage.[13,18,20,23] Mouse brains are roughly 10mm across compared to 120mm in humans. A voxel size of 100m3 or less is thus required to achieve resolution comparable to the 1mm3 voxel size in human neuroimaging. Some recent work has obtained 3D whole-brain MT images with good resolution (200x200x230m3[12] or 117m isotropic[19,24]), although results presented included only either single-slice or region-of-interest (ROI) analysis. While ROI analysis is useful for boosting SNR and performing coarse regional evaluations, it necessarily introduces exaggerated partial-volume dilution and obscures fine regional and structural variations. This latter point is of particular interest because pathology and morphology are known to be highly heterogeneous both regionally and across animals in the cuprizone model.[10C13,15,25C27] In this study we investigated non-invasive methods of characterizing demyelination and remyelination in-vivo. We employed T2-weighted and magnetization transfer imaging sequences, established semi-quantitative MRI techniques designed to achieve whole-brain coverage with exceptional spatial resolution (100m isotropic), to elucidate the spatial distribution of acute cuprizone-induced demyelination, and subsequent remyelination, in adult C57BL/6 male mice. Gold-standard histological analyses were used to evaluate the extent to which MTR was a specific measure of myelin content in-vivo. We thus confirm.